Noncircular transient fluid fuel injector control channels in propellant injector combustion systems

Abstract

A fuel injector system for combustion engines and motors, such as pulsed bipropellant thrusters, includes noncircular fuel and oxidizer injectors at the ends of respective dribble channels for controlling the mixture ratio of the propellants passing into a combustion chambers for maintaining a desire or ideal mixture ratio as determined by the cross-sectional area of the injectors well suited for pulse combustion fuel injector systems.

Description

FIELD OF THE INVENTION[0001]The invention relates to the field of combustion engines and motors. More particularly, the present invention relates to sizing of fuel and oxidizer dribble channels for improved propellant injection and combustion.BACKGROUND OF THE INVENTION[0002]In-space propulsion is an important part of most space missions, accounting for an average of 40% of the launched mass of unmanned systems. Pulsed bipropellant thrusters are commonly used on spacecraft for in-space propulsion. Short-pulse operation is particularly useful for attitude control, the figure of merit being the minimum impulse bit. Propellant consumption in limit cycle operations is particularly sensitive to the minimum impulse bit. A rough estimate of the size of the minimum impulse bit of a thruster is the steady state force generated times the pulse width, but significant deviations from this concept are found experimentally. Pulse widths as short as 0.01 s are used operationally. The efficiency of...

AI Technical Summary

Benefits of technology

[0012]An object of the invention is to improve the efficiency of bipropellant combustion systems.

[0016]The invention is directed to modifying the cross-sectional area of propellant injectors. The injector orifices are shaped to insure that the design mixture ratio, which is achieved in steady state operation, is also achieved in the shortest burn times. At least one of the injectors is noncircular or the number of fuel and oxidizer channels is unequal to achieve synchronized flow response. Alternatively, the injectors can be shaped to implement a hotter mixture ratio for short burn times that will achieve design thrust levels more quickly, while still delivering the design mixture ratio for longer burns. The synchronization of propellant response times also allows the reduced flow in short pulse operation of the bipropellant thruster to be used to throttle the thruster over a wide range without damaging the engine or contaminating the spacecraft with the products of incomplete combustion. These and other advantages will become more apparent from the following detailed description of the preferred embodiment.

Problems solved by technology

Propellant consumption in limit cycle operations is particularly sensitive to the minimum impulse bit.

Incomplete combustion of pulsed bipropellant thrusters and can lead to condensed phase reaction intermediates that can contaminate spacecraft surfaces, and even cause erosion.

In some cases, the reaction intermediates formed in incomplete combustion can lead to hard-starts, or engine damage.

For a short pulse meant to deliver the minimum impulse bit, however, the combustion chamber may never reach steady state conditions within the pulse.

Incomplete combustion could be one of the factors contributing to the low efficiency and high variability of pulsed thrusters, as well as the generation of contaminants.

For missions where the required total impulse is less than 45,000 N-s monopropellant systems are used because the propellant savings does not justify the increased complexity.

The few millisecond oxidizer lead provided by a smaller oxidizer dribble volume in the current designs is not enough to compensate for this mismatch.

The fuel rich mixture results in lower combustion temperatures, and incomplete combustion, which causes several problems.

Incomplete combustion can lead to the accumulation of combustion intermediates.

The fuel oxidizer reaction products produce undesirable high-energy condensation.

The products have been linked to several problems with thrusters, such as hard starts, and even damage to the thruster body.

The fuel oxidizer reaction products can also contaminate other spacecraft surfaces where there is a lower vapor pressure than fuel, oxidizer, or combustion products.

Unequal propellant response times can also lead to combustion instability.

Prior propellant injector systems have used conventional dribble channels and injectors producing mismatches in fuel and oxidizer delivery, contamination, and spikes in the combustion performance.

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